Refactor String model class

Refactors String model class based on JDK 10.0.1 source.

* Add support for JEP 254: Compact Strings, which fixes
    [junit] java.lang.NoSuchFieldError: java.lang.String.COMPACT_STRINGS

* Refactor String#contentEquals(java.lang.CharSequence) as the current
implementation only handles UTF16

Author: gayanW

src/classes/modules/java.base/java/lang/String.java

@@ -63,6 +63,10 @@ public final class String
 
 	private static final long serialVersionUID = -6849794470754667710L;
 
+	static final boolean COMPACT_STRINGS;
+	static {
+		COMPACT_STRINGS = true;
+	}
 
 	private static final ObjectStreamField[] serialPersistentFields =
 			new ObjectStreamField[0];
@@ -79,18 +83,13 @@ public String(String original) {
 	}
 
 	public String(char value[]) {
-		this(value, 0, value.length, null);
+		this(value, 0, value.length);
 	}
 
-	public String(char value[], boolean share) {
-		this(value, 0, value.length, null);
-	}
-	
 	public String(char value[], int offset, int count) {
 		String proxy=init(value,offset,count);
 		this.value=proxy.value;
 		this.coder=proxy.coder;
-		this.hash=proxy.hash;
 	}
 
 	private native String init(char[] value, int offset, int count);
@@ -99,7 +98,6 @@ public String(int[] codePoints, int offset, int count) {
 		String proxy=init(codePoints,offset,count);
 		this.value=proxy.value;
 		this.coder=proxy.coder;
-		this.hash=proxy.hash;
 	}
 
 	private native String init(int[] codePoints, int offset, int count);
@@ -119,13 +117,10 @@ public String(byte ascii[], int hibyte) {
 		this(ascii, hibyte, 0, ascii.length);
 	}
 
-
-
 	public String(byte bytes[], int offset, int length, String charsetName){
 		String proxy=init(bytes,offset,length,charsetName);
 		this.value=proxy.value;
 		this.coder=proxy.coder;
-		this.hash=proxy.hash;
 	}
 
 	private native String init(byte bytes[], int offset, int length, String charsetName);
@@ -151,8 +146,7 @@ public String(byte x[], int offset, int length, Charset cset) {
 		this.coder = result.coder;
 	}
 
-	public String(byte bytes[], String charsetName)
-			throws UnsupportedEncodingException {
+	public String(byte bytes[], String charsetName) throws UnsupportedEncodingException {
 		this(bytes, 0, bytes.length, charsetName);
 	}
 
@@ -164,42 +158,30 @@ public String(byte bytes[], int offset, int length) {
 		String proxy=init(bytes,offset,length);
 		this.value=proxy.value;
 		this.coder=proxy.coder;
-		this.hash=proxy.hash;
 	}
 
-
 	private native String init(byte bytes[], int offset, int length);
 
 	public String(byte bytes[]) {
 		this(bytes, 0, bytes.length);
 	}
 
-
 	public String(StringBuffer x) {
 		this(x.toString());
 	}
 
-
 	public String(StringBuilder x) {
 		this.value = Arrays.copyOf(x.getValue(), x.length());
 		this.coder = x.coder;
 	}
 
 	String(char[] value, int off, int len, Void sig) {
-		if (len == 0) {
-			this.value = "".value;
-			this.coder = "".coder;
-		} else {
-			byte[] val = StringUTF16.compress(value, off, len);
-			if (val != null) {
-				this.value = val;
-				this.coder = LATIN1;
-				return;
-			}
+		this(value, off, len);
+	}
 
-			this.coder = UTF16;
-			this.value = StringUTF16.toBytes(value, off, len);
-		}
+	String(byte[] value, byte coder) {
+		this.value = value;
+		this.coder = coder;
 	}
 
 	@Deprecated
@@ -213,32 +195,21 @@ public int length() {
 	public boolean isEmpty() {
 		return value.length == 0;
 	}
-	@Override
-	public char charAt(int index) {
-		if ((index < 0) || (index >= value.length)) {
-			throw new StringIndexOutOfBoundsException(index);
-		}
-		return this.isLatin1() ? StringLatin1.charAt(this.value, index) : StringUTF16.charAt(this.value, index);
-	}
 
+	native public char charAt(int index);
 	native public int codePointAt(int index);
 	native public int codePointBefore(int index);
 	native public int codePointCount(int beginIndex, int endIndex);
 	native public int offsetByCodePoints(int index, int codePointOffset);
 	native public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin);
-	native void getChars(char dst[], int dstBegin);
 
 	@Deprecated
 	native public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin);
-	native public byte[] getBytes(String charsetName)
-			throws UnsupportedEncodingException;
+	native public byte[] getBytes(String charsetName) throws UnsupportedEncodingException;
 
 	public byte[] getBytes(Charset x){
-		// No Charset model.
-		if (x == null){
-			throw new NullPointerException();
-		}
-		return StringCoding.encode(x, this.coder, this.value);
+		if (x == null) throw new NullPointerException();
+		return StringCoding.encode(x, coder(), value);
 	}
 
 	native public byte[] getBytes();
@@ -251,6 +222,26 @@ public boolean contentEquals(StringBuffer stringBuffer){
 		}
 	}
 
+	private boolean nonSyncContentEquals(AbstractStringBuilder abstractStringBuilder) {
+		int len = length();
+		if (len != abstractStringBuilder.length()) {
+			return false;
+		}
+		byte v1[] = value;
+		byte v2[] = abstractStringBuilder.getValue();
+		if (coder() == abstractStringBuilder.getCoder()) {
+			int n = v1.length;
+			for (int i = 0; i < n; i++) {
+				if (v1[i] != v2[i]) {
+					return false;
+				}
+			}
+		} else {
+			return isLatin1() && StringUTF16.contentEquals(v1, v2, len);
+		}
+		return true;
+	}
+
   native static boolean equals0 (char[] a, char[] b, int len);
 
   /**
@@ -262,21 +253,28 @@ public boolean contentEquals (CharSequence charSequence){
 			return false;
 		}
 
-		// that should be the common case (String)
-		if (charSequence.equals(this)){
-			return true;
+		// cs is a String
+		if (charSequence instanceof String) {
+			return equals(charSequence);
 		}
 
-		// we can do that natively, too
+		// cs is a StringBuffer, or StringBuilder
 		if (charSequence instanceof AbstractStringBuilder) {
-			byte[] val = ((AbstractStringBuilder) charSequence).getValue();
-			byte coder = ((AbstractStringBuilder) charSequence).getCoder();
-			assert coder == UTF16 : "Currently only UTF16 is supported for String comparision with an instance of type AbstractStringBuilder";
-			return StringUTF16.contentEquals(this.value, val, this.length());
+			if (charSequence instanceof StringBuffer) {
+				synchronized (charSequence) {
+					return nonSyncContentEquals((AbstractStringBuilder) charSequence);
+				}
+			} else {
+				return nonSyncContentEquals((AbstractStringBuilder) charSequence);
+			}
 		}
 
 		// generic CharSequence - expensive
 		int n = charSequence.length();
+		if (n != length()) {
+			return false;
+		}
+
 		byte[] val = this.value;
 		if (isLatin1()) {
 			for (int i = 0; i < n; i++) {
@@ -401,6 +399,10 @@ public static String valueOf(char character) {
 	native public static String valueOf(double d);
 	public native String intern();
 
+	byte coder() {
+		return COMPACT_STRINGS ? coder : UTF16;
+	}
+
 	private boolean isLatin1() {
 		return this.coder == LATIN1;
 	}